1. Technical Field
The present invention relates to an improvement of production steps of a methyl ethyl ketone-modified resorcinol-formalin resin (hereinafter referred to as an “MEK-modified resorcinol-formalin resin” for brevity) and a reuse method of specific raw materials (methyl ethyl ketone (hereinafter referred to as “MEK” for brevity), methanol and calcium chloride) used in the production.
More particularly, in the present invention, resorcinol, water, hydrochloric acid and formalin are used in addition to the above raw materials, and the present invention relates to a recovery and reuse method of the above specific raw materials from a waste liquid containing these chemical substances with good efficiency.
2. Background Art
It is reported that in the production steps for an MEK-modified resorcinol-formalin resin by adding given amounts of calcium chloride, water, MEK, resorcinol and hydrochloric acid as raw materials, completely dissolving those, and adding dropwise formalin thereto to conduct a reaction, an MEK-modified resorcinol-formalin resin was produced by separating the solution into an aqueous layer containing calcium chloride and an MEK layer, removing calcium chloride precipitated by azeotropic dehydration of the MEK layer by pressure filtration, and after solvent substitution of water and MEK by distillation, adjusting the pH with an aqueous ammonia (for example, Patent Document 1).
Conventionally, a resorcinol-formalin resin has high curing rate, and is therefore used in adhesives, plywood, laminated woods, surface coating agents and the like. In particular, the resin has excellent adhesion to rubbers or fibers, and is therefore used as an adhesive for tires and an adhesive for rubber hoses.
Methanol is contained as a stabilizer in formalin in an amount of from several % to about 10%, and formalin is used as a condensation agent in producing an MEK-modified resorcinol-formalin resin, and is therefore an essential raw material, However, a waste liquid from each production step contains a large amount of impurities other than methanol as the stabilizer, and recovery of methanol from an aqueous layer separated from an MEK layer after a liquid-liquid heterogeneous reaction by dropwise addition of formalin is an indispensable operation.
Furthermore, it is known that when a slight amount of inorganic salts such as calcium chloride remains in an MEK-modified resorcinol-formalin resin, adhesion to tires, fibers or the like, in which it is used as an adhesive, is deteriorated. Removal method of the calcium chloride is that calcium chloride dissolved in water contained in the MEK layer is precipitated by azeotropic dehydration, and the precipitate is then treated with pressure filtration.
However, the removal method of calcium chloride by pressure filtration is cumbersome and takes time, and the removal effect is not sufficient. Thus, there is room for improvement.
Patent Document 1: WO2005/035611A1